EP0703424A1 - Heat exchanger constructed as an assembly of plates - Google Patents

Abstract

The present invention relates to plate-type heat exchangers, such as are used, for example, in water-cooled embodiments of charge air coolers with air-side fin plates (16). In order to avoid the undesired and damaging thermal expansion effects in the heat exchanger that occur during unsteady operation of a charge air cooler (1, 1 ', 2, 3), the invention proposes to cool the otherwise completely brazed cooler block (8) in two or along a plane parallel to the plate levels to divide several sub-blocks (20, 21). If the sub-blocks (20, 21) are combined at a mutual distance (a) to form a radiator block assembly (8), each sub-block (20, 21) receives a free space in the transverse direction, which compensates for the heat-related transverse expansions of the individual blocks (20), (21) . <IMAGE>

Description

The invention relates to plate-type heat exchangers, in particular plate-type heat exchangers in design guides as water-cooled charge air coolers with air-side finned plates, according to the preamble of patent claim 1.

Plate heat exchangers basically consist of a number of walls which guide the air or liquid flow to be cooled and coolant flows in such a way that no mixing can take place between these two media. The heat exchange thus takes place directly via the walls and fins, which generally consist of a good heat-conducting metal. To minimize construction costs, the media flows are carried out according to the cross or cross counterflow principle.

With regard to their basic structure, water-cooled plate heat exchangers can be divided into round tube cooler systems and flat tube cooler systems. Of these two cooling systems, the flat tube cooler system has a more favorable ratio between cooling capacity and pressure loss on the charge air side, since flat tubes, due to their aerodynamic shape, cause lower pressure loss values on the charge air side and can therefore be finned more intensively. In this construction principle of a generic plate heat exchanger, water channels and air duct channels are therefore combined in a regular arrangement as a stratification of several plates to form a cooler block and completely brazed to one another. The radiator block thus defined in its shape is inserted and welded fully pre-assembled in a receiving frame, which at the same time forms the water collection boxes through which coolant flows and guide devices for the air to be cooled.

This principle structure of a cooler block surrounded by coolant, which is itself flowed through by the hot medium to be cooled and thereby heats up accordingly, generally leads to large thermal stresses within the entire structure. This construction with a cooling jacket on the outside and a hot radiator block matrix on the inside inevitably results in a temperature gradient from the inside of the cooling block to the cooling jacket during operation of the heat exchanger. As a result of the resulting different high temperatures, the cooler block experiences an expansion hindrance due to the colder water collection boxes leads to deformations of the connection points of the water channels welded to the water collection boxes.

In order to contain this temperature-related expansion of the radiator block, the side walls were also cooled by the coolant in more recent versions of plate heat exchangers, in particular the charge air cooler. This measure enabled the longitudinal expansion of the individual panels and the expansion behavior of the side walls to be coordinated with one another, but temperature-related expansion differences still occur between the cooler block and the water tanks in a direction perpendicular to the panel plane. The cause of this thermal expansion occurring in the transverse direction is the lamellae of the charge air-carrying lamella plates, which are meandered between two water channels and brazed to the water channel walls. The linear expansion of the fins leads to a temperature-dependent expansion of the individual plate layers, the thermal expansions of the individual lamella layers adding up over the width of the radiator block.

Since the cooler block - and in particular the connection points of the water channels - are welded firmly to the water tanks and therefore do not allow any relative displacement, any increase in the temperature of the cooler block inevitably leads to a deflection of the channels in the transverse direction. The deflection of the individual channels in turn leads to changes in angle at the connection points, which consequently increase with increasing temperature difference from air to water, that is to say the media flowing through the heat exchanger, and with increasing cooler width, that is to say the number of plate layers.

Due to these temperature-related deformations, large charge air temperature fluctuations are generated, especially with charge air cooling of highly charged engines and large load amplitudes, by means of which the fatigue strength of the materials used is reached too early for operating load collectives with a large number of load cycles. Undesired consequences of this are damage to the connection points with transfer of the media.

Another source of damage for the intercooler in plate construction are the temperature-related deformations of the air fins on one or more Lamella rows represent. While, as described above, the individual plate layers bend in the transverse direction when the temperature rises, the individual thermal expansions add up across the transverse direction up to the side walls. Due to the temperature-related expansion of the water boxes, which are therefore considered to be stiff compared to the cooler block, these heat displacements increasingly lead to deformations of the slats themselves in the air lamella layers lying further outward. The lamella layers are pressed against the coolant-cooled side walls, which are to be regarded as stiff, and in some cases plastically deformed . However, since the lamellar loops are firmly soldered at their vertices to the adjacent water channel wall and thus their position is clearly defined, the lamellae squeezed at high temperatures experience elastic and then plastic expansion when the air cools, i.e. at the charge air temperature, as described above , in the event of frequently occurring load changes in the motor, the fatigue strength of the lamellar materials is exceeded and the lamellas break. The resulting U-shaped lamella pieces, which are only soldered in at one point, are caused to vibrate by the charge air flowing through them and tear away. In this way, there is a risk that the lamella pieces get into the combustion chamber and / or wear through or tear through the relatively thin walls of the water channels and thus lead to damage.

The invention is based on the technical problem of further developing plate heat exchangers of the generic type in such a way that damage due to thermal expansion effects is avoided.

This problem is solved in a generic plate heat exchanger by the characterizing features of claim 1.

The dependent claims contain expedient developments of the invention.

According to the invention, the otherwise firmly brazed structure of the cooler block is interrupted one or more times parallel to the plate level. This interruption of the dimensionally rigid radiator block along a plate surface prefers a planned structural weakening of the corresponding air lamella plate layer. The slat loops, which are otherwise soldered on both sides to the adjacent water channel walls, together form a rigid sandwich structure, the The reason for this is that occurring forces, as in the case described, thermal expansion stresses are passed on to the overall structure and absorbed by it as a whole. Because a targeted weakening of this overall structure is now provided, the summation effect of the individual forces is achieved in many subtotals in accordance with the intended number of subdivisions. Seen across the entire structure of the cooling matrix, a quasi outward migration of the heat shift into the outer lamella layers is thus interrupted as planned; as a result, the large amplitude of displacement in the outer layers can be divided into smaller amounts absorbed by several lamella layers.

In contrast to the large amount of squeezing of the outer lamellae that has occurred up to now, the thermal expansion can therefore be divided into smaller amounts according to the invention.

As a result of this weakening, the intended weak point of the cooling structure itself, according to the invention, is no longer able to pass on the forces acting on it to the neighboring structure, but is plastically deformed, as previously the outer lamella layers. In contrast to the previous deformations, the deformation of the weak point according to the invention now represents a calibration process in which the cooler block automatically adapts to the thermal expansion conditions occurring in its structure and thereby does not take any permanent damage.

In the predetermined weak point, the fins are also plastically deformed more at the apex of the deflection and less strongly in the direction of the connection points, but this deformation occurs only once during the calibration process and then only in one direction. Due to the structural interruption according to the invention, there is no longer a non-positive connection along the parting plane between the adjacent plate layers, so that in the specific case the previously plastically compressed fins are no longer subject to plastic expansion when the cooler matrix cools down. After the calibration process has taken place, the lamellae of the parting plane according to the invention now only have to withstand a swelling load and are no longer subjected to a permanent alternating stress as before. The swelling load can be easily compensated for by the elastic deformability of the slats.

In principle, the division of the cooler matrix into two or more narrower, but not soldered-together sub-blocks can be provided without or with a small, intermediate distance. Regardless of the distance provided, the deflection and angle change of the water channels are accordingly only 1/2 to 1 / n of the previous values. This means that, independently of the embodiment of a radiator block according to the invention, selected lamella layers are only mechanically stressed to such a small extent that material failure due to thermal expansion can be significantly reduced.

In embodiments of the invention, in which the individual partial blocks are provided with a mutual spacing, the dimensioning of this spacing can be used to direct the extent of the plastic deformation of the lamella layer which is desired once during the calibration process. In addition, however, the one-off plastic deformation can be completely ruled out by selecting the appropriate distance.

Such a design of the radiator block offers a reliable precaution against thermal expansion-related damage to the charge air cooler and / or the engine itself, in particular in cases of application with extreme temperature fluctuations.

In contrast, in applications with lower temperature fluctuation amplitudes, a large distance provided can markedly deteriorate the cooling capacity of the heat exchanger, since a relatively large charge air mass flow can flow through the cooling matrix almost unhindered at this point. A remedy for this performance limitation is provided by a further preferred embodiment of the invention, in which it is provided that the cooler matrix is not placed along a contact plane between the water channel and the adjacent lamella plate, but instead two narrower layers instead of the lamella layer soldered on one side, each soldered on one side to one of the opposite water channel walls Arrange lamellar layers that together penetrate the separating gap between two sub-blocks with lamellas without mutual positive connection. If thermal expansions occur, in this embodiment the two lamella layers directed towards one another are pushed onto one another and partially into one another. Due to the flexural elasticity of the lamellae soldered on one side, they are not necessarily plastically deformed, but instead yield laterally under elastic and / or one-time plastic deformation and can thus be pushed into one another.

Figur 1:

eine Querschnittdarstellung eines ersten Ausführungsbeispiels mit Abstand im Ausgangszustand;

Figur 2:

das Ausführungsbeispiel aus Figur 1 im Betriebszustand ohne plastische Verformung;

Figur 3:

ein zweites Ausführungsbeispiel der Erfindung im Betriebszustand nach dem Kalibriervorgang;

Figur 4:

ein drittes Ausführungsbeispiel der Erfindung mit Doppellamellenschicht.

Further more expedient refinements of the invention and a more detailed explanation are contained in the following description, which relates to three exemplary embodiments shown in the drawing. The drawing shows:

Figure 1:

a cross-sectional view of a first embodiment with distance in the initial state;

Figure 2:

the embodiment of Figure 1 in the operating state without plastic deformation;

Figure 3:

a second embodiment of the invention in the operating state after the calibration process;

Figure 4:

a third embodiment of the invention with double lamella layer.

A total of three exemplary embodiments of the water-cooled intercooler according to the invention are shown in FIGS. 1 and 2, 3 and 4. In all three exemplary embodiments or in all four figures, for the sake of simplicity, the same parts are provided with the same reference numbers.

All three exemplary embodiments are shown in the form of a cross-sectional view with a view of the air inlet into the cooler block 8 and the coolant flows through them in the vertical direction; here inflow 9 and outflow 10.

In Figure 1, an inventive charge air cooler 1 is shown in its basic structure. The charge air cooler 1 essentially consists of a cooler block 8, at the upper and lower block ends of which an upper water collection box 4 and a lower water collection box 5 are welded. Laterally, the cooler block 8 is surrounded by a side part 6 and 7, which are connected in a liquid-conducting manner to the upper water tank 4 and the lower water collecting tank 5. The upper water collecting box 4 and lower water collecting box 5 together with the side parts 6, 7 thus form a receiving frame through which the coolant, here water, flows, for the radiator block 8 inserted therein and fixed by means of corresponding weld seams 13.

The cooler block 8 consists essentially of a large number of flat water channels 11 and air channels 12. The water channels 11 are formed by wall plates 14 and rods 15, while the air channels are formed by lamella plates 16. The lamellar plates 16 are composed of a plurality of lamellar strips arranged next to one another, these being produced in a known manner from a thin, good heat-conducting material which is shaped in a meandering manner in such a way that longitudinal channels, viewed from the end edge of the lamellar plate 16, are formed, whose width corresponds essentially to the thickness of the lamella plate. Several of these plate plates 16 are arranged in the radiator block 8 alternately with water channels 11 at regular intervals and soldered together to form the radiator block 8. All cooler power supplies are made of aluminum and are preferably connected to each other by hard soldering. In principle, the components can consist of unalloyed and alloyed steels, brass or copper. Of these, non-ferrous metal designs offer the greatest cooling performance advantages, but their manufacture is complex and expensive.

The cooler block 8 composed of the so-called plates 11, 12 mentioned above is usually prefabricated as an assembly and then inserted into the coolant frame, which is also produced separately, from the upper water tank 4, lower water tank 5, and the side walls 6, 7.

In the radiator block 8, a lamella plate 16 is arranged between two wall plates 19 and is brazed to them via linear solder seams along the apex line of the lamellae. This flat, double-sided soldering of the fins 12 to the wall plates 19 forms from the considered slack wall surfaces 19 and finned plates 16 a rigid sandwich structure which has sufficient rigidity to withstand the back pressure fluctuation occurring in unsteady engine operation in a wide range in front of the charge air cooler Hold up.

Several of these lamella plates, which are prefabricated in this way, are arranged next to one another in the manner described above and are each connected to the completely brazed radiator block 8 via a water channel 11 provided between them, the width of which is predetermined by means of rods 15. The upper and lower open side surfaces of the lamella plate 16 are each sealed by means of a correspondingly wide strip 22, so that no cooling water from the cooling water boxes when in the inserted state 4, 5 can get into the air channels 12. In each case, between two adjacent strips 22, the water channels 11 are conductively connected to the lower water tank 5 and the upper water tank 4. To this end, the water channels 11 are either welded to the water boxes 4, 5 along the connection points or are also brazed. Regardless of the type of connection, these connection points are usually provided as rigid connections, wherein the best possible heat transfer between the wall surfaces 19 and the boxes 4, 5 is to be achieved.

In the exemplary embodiment shown in FIG. 1, the cooler block 8 according to the invention consists of two sub-blocks 20 and 21, which are connected to one another at a distance a via corresponding connecting plates 24, 25.

It is essential here that the lamella plate 26 of the sub-block 21 is only soldered on one side to the wall plate 27 of the adjacent water channel 11. As a result, the lamellae of this lamella plate 26 protrude freely into the air duct 28 which is wider according to the invention. At the same time, the position of the partial blocks 20, 21 relative to one another and with respect to the water boxes 4 and 5 is clearly defined by these connecting plates 24 and 25.

The structural relationships described above and shown in FIG. 1 are present in the initial state, that is to say the cold state, in the case of a heat exchanger according to the invention. If the operating conditions of the charge air cooler change as a result of a changed load requirement on the engine, the charge air cooler 1, 2, 3 is flowed through by a charge air flow at a higher temperature. This hot air flow flows through the air channels 12 along the fins arranged therein and heats them up to the air temperature within a few seconds. The heat quantity of the charge air flow transferred to the fins is absorbed via heat conduction by the cooling water flowing through the water channels in the direction from the lower water collection box 5 to the upper water collection box 4 and transported out of the charge air cooler 1. As a result of their heating, the fins bend in the direction of the arrow 18, that is to say in the transverse direction of the charge air cooler 1 ′ shown. Due to the meandering guidance of the lamellae within a lamella plate 16, elongations in the direction of flow of the cooling water are compensated for in a constructive manner. The longitudinal expansion of the lamellae in the transverse direction 18, on the other hand, has a direct effect on widening the lamella plate thickness, since, as already described above, the lamellae are firmly connected or brazed to the adjacent sheet metal walls 19 along their apex lines are. Due to the stiffening of the lamella plates 16, which is intended on the one hand by soldering, on the other hand, there is now the disadvantage that the temperature-related elongation of the lamella flanks has an immediate effect on increasing the width of the lamella plate 16.

Since the water channels 11, as described in Figure 1, are positively and non-positively connected to the water collection boxes 4 and 5 and due to the large amount of coolant in the immediate vicinity there is also a correspondingly low thermal expansion, the thermal expansion of the fins leads in the direction of Arrow 18 finally to a deflection of the slat plate 16 in the transverse direction. Since the individual plates 16, 11 are brazed to one another, the thermal expansions of the individual plates add up within a block 8.

In the heat exchanger shown in FIG. 2 in the operating state with a two-part cooler block 8 and a spacing a between, it can be seen very clearly how the individual blocks each bend or widen in the transverse direction. So far the response of the charge air cooler corresponds to that of known charge air coolers. Due to the division of the cooler block 8 according to the invention in the form shown in FIG. 1, the summation of individual thermal expansions is specifically interrupted. Due to the distance a between the water channel 29 and the lamella plate 26 provided according to the invention, the wide air channel 28 thus created serves as a buffer for the expansion of the partial blocks 20 and 21 taking place on both sides, due to the heating. At the same time, the cooling block 8 is divided into two in this embodiment , both the deflection and the change in angle of the water channels and air channels halved at least in the lamella plates 16 adjacent to the side parts 6 and 7.

If, as shown in FIG. 2, spacings are also provided on both sides of the radiator block 8 and between the side parts 6 and 7, then even the outermost lamella plates 16 do not experience any deformation if they are bent accordingly.

In the embodiment shown in FIG. 2, the distance a is dimensioned such that the heat-related expansion of the outermost lamella layer 26 of the partial block 21 together with the bending of the water channel 29 caused by elongation correspond exactly to the distance a. Because such a dimensioning of the distance only The measurement of the distance is associated with high costs in a purely imperial way.

An embodiment as shown in FIG. 3 helps, in a further development of the invention, to save this cost. In this embodiment, the two sub-blocks 20, 21 are not combined at a mutual distance from one another to the cooler block 8, but the lamella plate 26 is not soldered to the water channel 29 without a distance from it. Due to this missing soldering of the lamella apex of the lamella plate 26, it has a lower rigidity than the other lamella plates 16, which are brazed on both sides. If thermal expansions now occur in the operating state, the sub-blocks 20 and 21 also expand independently of one another, as before , however, the stresses due to thermal expansion cannot be transmitted from the less stiffened lamella plate 26. Thus, the lamella plate 26 according to the invention represents a weak point in the radiator block assembly, which, as the weakest link, compensates for the heat-related expansions of both blocks along the parting plane in that their lamellae are elastically deformed in the counterpressure to the water channel 29 according to the bending line. If the radiator block 8 subsequently cools down again, the deflection of the individual plates decreases accordingly, but the fins of the finned plate 26 remain permanently plastically deformed. It is essential to the invention that during the cooling process there is no longer any plastic reshaping of the fins and therefore they are no longer deformed even when the charge air cooler is heated again, provided that no other temperature maximum is reached.

A third exemplary embodiment is shown in FIG. 4. In this exemplary embodiment, too, the cooler block is divided into two sub-blocks 20 and 21 and is mounted at a distance from one another in the coolant receiving frame. In contrast to the previously described exemplary embodiment, in this embodiment, however, a lamella plate 26 and a water channel 29 do not meet one another, but instead there are lamella plates 38 and 39 on both mutually facing side surfaces of the partial blocks 20 and 21 in a manner as previously in the case of the figure 3 embodiment shown, the lamella plate 26 is fixed on one side. Such a configuration ensures that charge air cannot flow freely through the charge air cooler 3 in the air duct 28, in particular without cooling. Because of this arrangement of lamella plates 28 and 39 on both sides, the air duct 28 is also included Heat transfer means traversed, although a transfer of the heating-related shift from one to the other block 20, 21 does not take place. The lamella strips 38 and 39 can be made significantly smaller than the other lamella strips 16. A special case is a design of the lamella strips 38 and 39, in which the width of the strips is half that of the other lamella strips 16, so that both together have the same plate thickness as the other lamella plates.

If, with appropriate heating of the radiator block 8, the lamella plates 38 and 39 meet as a result of the thermal bending, these are either pushed into one another with elastic deformation, if necessary, or, however, the lamellae 38, 39, which are each less rigid, are plastically deformed accordingly. However, since only one-dimensional loading of the fins takes place here in the case of plastic deformation, the material limits are not reached and, as a result, thermal expansion-related disturbances of the charge air cooler 3 are avoided.

Reference list

1.

Intercooler

2nd

Intercooler

3rd

Intercooler

4th

Upper water collection box

5.

Lower water collection box

6.

Side panel

7.

Side panel

8th.

Radiator block

9.

Inflow of coolant

10th

Drain coolant

11.

Water channel (coolant)

12th

Air duct

13.

Welds

14.

sheet

15.

Rod

16.

Slat plate

17th

Solder joint

18th

Arrow direction

19th

Wall panel

20th

Partial block

21.

Partial block

22.

strip

23.

Junction

24th

Connecting plate

25th

Connecting plate

26.

Slat plate

27.

Wall panel

28

Air duct

29.

Water channel

38.

Slat plates

39.

Slat plates

a.

Plate spacing

Claims (5)

Plate-type heat exchanger, especially water-cooled intercooler, with: 1. a radiator block (8) consisting of substantially parallel to each other arranged at regular intervals a) sheets (14) and rods (15) which form water channels (11), b) lamella plates (16) which form air channels (12), c) side parts (6), (7), and 2. water collection boxes (4), (5) which are attached to the water supply (9) and water-stirring (10) block ends in a liquid-tight manner, characterized in that the cooler block (8) is subdivided into two or more sub-blocks (20), (21) along one or more planes parallel to the plane of the plate. Heat exchanger according to Claim 1, characterized in that the partial blocks (20), (21) are arranged at a mutual distance (a) from one another. Heat exchanger according to Claim 2, characterized in that the distance (a) is dimensioned such that the plates (26), (29) lying opposite one another of two partial blocks (20), (21) are due to the fact that the fin plates (16 , 26) touch the resulting thermal expansion. Heat exchanger according to one of claims 1 to 3, characterized in that the cooler block (8) along a contact plane of the wall plate (19) of a water channel (29) of a first partial block (20) and an adjoining fin plate (26) of a second partial block (21 ) is divided. Heat exchanger according to claim 1 or 2, characterized in that the mutually facing plates of two adjacent partial blocks (20), (21) are designed as lamella plates (38), (39).

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